Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and Media Access Control (MAC) specifications for implementing Wireless Local Area Network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
WLAN devices are currently being deployed in diverse environments. These environments are characterized by the existence of many Access Points (APs) and non-AP stations (STAs) in geographically limited areas. Increased interference from neighboring devices gives rise to performance degradation. Additionally, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. Video traffic, in particular, is expected to be the dominant type of traffic in WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance.
A WLAN device typically employs a carrier sense mechanism to determine whether it can transmit data over a wireless medium. The distributed nature of 802.11 WLANs makes the carrier sense mechanism very important for reducing the amount of collisions in the WLAN. The physical carrier sense mechanism of a WLAN device is responsible for detecting transmissions of other WLAN devices. However, it may be impossible for a WLAN device to detect all of the transmissions that may collide with its own transmission. For example, a WLAN device which is a long distance away from another WLAN device that is transmitting data may determine that the wireless medium is idle and begin transmitting data as well. To overcome such hidden node problems, a Network Allocation Vector (NAV) has been introduced. NAV maintains a prediction of future traffic on the wireless medium based on duration information captured from Physical Layer Protocol Data Units (PPDUs).
In a task group called Institute of Electrical and Electronics Engineers (IEEE) 802.11ax, High Efficiency WLAN (HEW) standardization is under discussion. The HEW aims at improving performance felt by users demanding high-capacity and high-rate services. The HEW may support uplink (UL) and downlink (DL) multi-user (MU) simultaneous transmissions, which includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) transmissions. The HEW may also support new Clear Channel Assessment (CCA) levels and deferral rules to improve Overlapping Basic Service Set (OBSS) operation in dense environments. Employing existing NAV techniques in the HEW may result in unintended inefficiencies.